1. Field of the Invention
The present invention relates generally to the field of apparatus and methods for surgically implanting artificial lenses in the human eye, and particularly to the implanting of artificial intra-ocular lenses in cataract surgery in place of diseased or damaged natural intra-ocular lenses as part of the lens implanting operation.
2. Discussion of the Background
Vision is the ability of the eye to form an image of an object and send the image to visual centers of the brain. In this process, light rays from the object pass through the cornea, the aqueous humor, the pupil, the intra-ocular lens (IOL) and the vitreous humor of the eye. These rays finally reach the retina where they stimulate the optic nerve cells. In turn, the optic nerve carries "messages" from the nerve cells to the visual cortex of the brain. The disc-shaped intra-ocular lens in the eye performs the same function as the lens of a camera and is responsible for focusing incoming light rays onto the retina, which is the image registering portion of the eye.
Injury and disease can affect the ability of an intra-ocular lens to perform its function of focusing and transmitting light rays. In particular, a cataract is a lessening of the transparency of the lens when the normally clear fibers, which comprise the lens, become cloudy. As a consequence, adequate light cannot reach the associated retina, and vision becomes increasingly blurred. Cataracts tend to be relatively common in persons over about 65 or 70 years of age; however, in younger persons a cataract may be present at birth or may result at any age from injury or disease. Diabetes can, for instance, cause cataracts to occur, as can glaucoma.
So far, as is known, there presently exists no treatments or medicines which can reverse a cataract and cause the cloudy lens fibers to become clear and transparent again. The only effective treatment for a cataract is surgical removal of the affected lens, and, until relatively recently, optical compensation for a removed lens was limited to strong glasses which were clumsy and heavy or contact lenses, although the latter are frequently incapable of providing sufficient focusing effect.
Medical technology has, however, recently advanced to the state that a diseased or damaged intra-ocular lens can now be replaced by an artificial intra-ocular lens which is surgically implanted in the eye behind the cornea after the natural lens has been removed. These artificial lenses can, like regular glasses or contact lenses, be specially made to correct other eye deficiencies and are, for example, commonly available in a variety of diopters. A typical medical protocol followed in replacing a diseased or damaged, natural intra-ocular lens with an artificial intra-ocular lens involves first making a small surgical incision or aperture in the cornea near its edge and to one side of the iris. The diseased or damaged natural intra-ocular lens is surgically removed through this corneal aperture, by such means as ultrasonically fracturing the lens and then extracting, as by the application of suction, the lens tissue. Next, an artificial replacement lens is carefully inserted into the eye through the same corneal aperture and is manipulated by the surgeon into the same position, behind the iris, previously occupied by the removed natural lens. According to the particular configuration of the artificial lens being installed, appropriate surgical techniques are then used to secure the artificial lens in its proper position in the eye. Finally, the incision made through the cornea is repaired.
For this type of surgical lens implantation procedure, it is known to use a flexible artificial lens, constructed of a material such as silicone, and to manually bend or curl the lens, for example, by forceps, into a tubular shape before insertion so that the size of the corneal aperture needed for insertion can be made as small as possible to minimize trauma to the eye. As soon as the artificial lens, when curled into tubular form, is inserted through the corneal aperture and is released, it uncoils on its own into its original flat, disc shape. This procedure of coiling an artificial lens into tubular form permits, by way of illustration, an artificial lens having a diameter of about one quarter inch to be inserted through a corneal opening only about one tenth of an inch across. The use of the above-described type of intra-ocular lens implantation technique is disclosed, for example, in U.S. Pat. No. 4,573,998 to T. Mazzocco, the disclosure of which is incorporated herein by reference.
Small artificial intra-ocular lenses are, however, extremely difficult to manually fold or curl into a small shape by forceps or other conventional medical instruments without scratching or otherwise damaging the lens. Moreover, the eye itself is so extremely delicate that even the merest touch of the tip of a surgical instrument or of a edge of the artificial lens on the one-cell layer of the endothelial lining on the posterior face of the cornea can tear some of the cells away from the corneal surface and permanently injure the eye.
Because of the difficulty in manually curling and inserting an artificial lens through a small incision in the cornea, various lens inserting instruments or apparatus have been developed or proposed for mechanically folding a flexible artificial lens and for then inserting the lens through the corneal incision into the eye. One such type of artificial lens inserting instrument believed to have been used in surgical lens implanting resembles a hypodermic syringe, in that it has a cylindrical barrel with an internal plunger and a converging, funnel-shaped insertion tip and a flanged chamber for holding the lens. A device of this nature is disclosed in U.S. Pat. No. 4,681,102.
In using such a syringe-type instrument, an artificial intra-ocular lens to be implanted in a patient's eye is placed in the instrument barrel and folded therein. An appropriate surgical incision is made in the patient's cornea and the natural intra-ocular lens is removed in a manner such as described above. The end of the insertion tip is then inserted through the corneal incision and the plunger of the instrument is depressed so as to push against a side edge of the artificial lens in the barrel. Depressing the plunger of the instrument forces the lens out of a cylindrical tip of the instrument and into the patient's eye.
A principal disadvantage associated with such types of artificial lens inserting instruments is that the lens tends to abruptly spring out of the tip. As has been emphasized above, an eye is extremely delicate and any abrupt ejection of the replacement lens from the inserting instrument into a patient's eye can result in the lens damaging delicate eye tissue and causing eye injury.
Even if the lens itself does not cause any eye injury in such circumstances, the abrupt ejection may result in the lens being incorrectly positioned in the eye, and the additional manipulation required to correctly position and align the lens may injure the eye. Further in this regard, it is also highly desirable that the lens transplant operation be completed as rapidly as possible and the corneal incision be quickly repaired so as to minimize trauma to the eye and reduce the possibility of infection. Therefore, the lens insertion instrument used should accurately position the artificial lens as the lens is inserted into the eye, so that the amount of subsequent manipulation of the lens is kept to a minimum.
For these and other reasons related to minimizing trauma to a patient's eye during and as a result of any intra-ocular lens transplant operation, improvements are needed to lens inserting apparatus and methods. Ideally, such improved apparatus should provide the ophthalmic surgeon who performs lens transplant operations complete and precise control of lens insertion into the patient's eye and should, therefore, eliminate or at least substantially reduce any tendency of the replacement lens to abruptly spring out of the insertion instrument into the eye during the insertion process. Additionally, such improved apparatus should leave at least one of the performing surgeon's hands free to hold other instruments, manipulate the patient's eye or otherwise assist with the operation.
The inventions described in applicants' previously referenced U.S. patent applications provide significant improvements in these respects. The apparatus and method disclosed in application Ser. No. 07/106,044 provides a convenient and simple means of receiving, holding and confining an intra-ocular lens, and one which provides an injector tip configuration and controlled movement of the lens out of the instrument in a manner to reduce abrupt springing of the lens out of the tip. The invention of the application referred to above and which is filed concurrently herewith shows and describes an entirely different technique wherein the lens is held and curled in what may be termed an "envelope" fashion and in which the lens as it moves out of the tip gently flowers out to eliminate such problems. The subject matter of the present application represents an improvement and modification of the apparatus and method disclosed in U.S. patent application Ser. No. 07/106,044 in that it provides improved lens holder and injector tip configurations, and means and methods of more gently passing the lens out of the tip and into the eye.